The present invention relates to an ink supply device for supplying ink to a print head in an image recording device of the ink jet type, and an image recording device using the ink supply device.
An example of the conventional ink supply mechanism used in the ink jet image recording device is disclosed in Published Unexamined Japanese Patent Application No. Hei. 3-41351. In the construction of the ink supply mechanism, a porous material is disposed within an ink tank. One end of the ink tank is connected to the print head through a filter disposed therebetween. The other end of the ink tank includes an air hole formed therein. In the ink supply mechanism thus constructed, air is introduced into the filter through a minute gap between the porous material and the inner wall of the ink tank, and the supply of ink from the ink tank to the print head is frequently interrupted.
To solve the problem, Published Unexamined Japanese Patent Application No. Hei. 2-34354 was proposed. A rib is disposed on the inner wall of the ink tank in a state that the rib comes in contact with the ink absorbing member. The rib functions to block the flow of air bubbles into the print head. Also in the technique of the publication, when the contact of the rib with the sponge is poor, air moves along the inner wall of the ink tank to reach the print head.
Published Unexamined Japanese Patent Application No. Sho. 57-2786 proposes another solution for the air-mixing problem. In the proposed solution, an air trapping chamber containing a porous material therein is placed in the ink path which connects the print head to the ink container. However, this solution is imperfect in that the fluid resistance of the porous material per se is large, and when air bubbles stay over the entire surface of the porous material, the fluid resistance is increased. Where the fluid resistance is large, it is impossible to supply a sufficient amount of ink to the print head engaging itself in a high speed printing operation.
Published Unexamined Japanese Patent Application No. Sho. 59-95152 discloses another air trapping means in which a filter cloth for trapping air bubbles is stuck onto one side of an elastomer plate. When air bubbles stay on the entire surface of the filter cloth, the fluid resistance is increased and the same problem arises. That is, the ink supply mechanism of the publication can also supply an insufficient amount of ink to the print head when it operates for print at a high speed.
Published Unexamined Japanese Patent Application No. Hei. 3-189157 makes another technical proposal on this problem. A hollowed needle is provided at the joint where the ink tank is connected to the print head. A porous material is contained in the hollowed needle for trapping air bubbles, dust, etc. The construction of this ink supply mechanism requires a small inside diameter of the hollowed needle in order to obtain a good connection at the joint. Where the inside diameter of the hollowed needle is reduced, the area of the opening for the porous material is also reduced, while the fluid resistance is increased. As a result, the ink supply mechanisms also fails to sufficiently supply ink to the print head operating at a high speed.
A possible way to solve the problems of those proposals in which the porous material or the filter are used for trapping air bubbles is to enlarge the filter particles size of the porous material an the filter. This possible solution also involves a problem. That is, when a large amount of ink is consumed in a maintenance work, for example, air bubbles pass through the porous material or the filter to enter the print head, possibly causing print defect.
Published Unexamined Japanese Patent Application No. Sho. 60-262654 discloses another ink supply mechanism in which a subtank is located between the ink tank and the print head, and ink is temporarily stored in the subtank and then supplied to the print head. The subtank is opened to the air, air is separated from ink in the subtank, and only ink is supplied to the print head. In the construction of the ink supply mechanism, there is a possibility that ink leaks from the subtank through its opening. Further, in order to keep the ink pressure in a negative pressure, the print heat must be located above the subtank. Such a design restriction is laid upon a designer.
A means for detecting an amount of ink left in the ink supply mechanism of the type in which a capillary member, such as the porous material, is disposed in the ink chamber, is disclosed in Published Unexamined Japanese Patent Application No. Hei. 3-138158. A transparent tube, shaped like C, as a left-ink detector, is provided on the side of the housing containing the capillary member. When ink of the capillary member is consumed an the liquid level of the left ink goes below the C-shaped transparent tube, ink is moved from the C-shaped transparent tube to the capillary member. The amount of the left-ink is detected on the basis of the decrease of the ink level. Another technique for detecting the amount of the left-ink is disclosed in Published Unexamined Japanese Patent Application No. Hei. 5-42680. In the publication, at least a part of the side wall of an ink tank filled with porous material is made of transparent material. Grooves of different capillary forces are formed on the inside of the transparent part or window. Such a construction that the left-ink detecting window is within the ink chamber filled with the porous material, is sensitive to a variation of the capillary forces of the porous material. Further, the grooves, which form the visually detecting part, are narrow. This makes it hard to detect the amount of left-ink. Further, in the construction, air inevitably enters the grooves when ink is filled into the ink tank. This requires additional work to remove ink from the grooves.